The invention relates to an apparatus for the regulation of the depth of the immersion of consumable electrodes into the slag of electroslag remelting furnaces, consisting of a system for detecting the actual resistance and the change of this resistance as the electrode is moved within the slag layer, and of a regulating means for the driving of the electrode, to which there is transmitted a signal corresponding to the actual resistance and, as a correction factor, a signal corresponding to the change of the actual resistance, measurement conductors for the melting current i and the melting voltage U being connected with a divider, in accordance with U.S. Pat. No. 4,075,414.
In the subject matter of the principal patent application, the quotient, EQU Resistance R=U/i=(Melting voltage/Melting current)
is formed in the divider and corresponds to the actual resistance in the slag blanket. This resistance, represented in relation to the depth of immersion of the electrode, results in hyperbolic curves which asymptotically approach the abscissas and the ordinates of the coordinate system. On the basis of the various apparatus and melting parameters, sets of curves are plotted which have a substantially similar course. These curves are also referred to as "immersion curves." Immersion curves, such as develop in the subject matter of the principal patent application, are also given for purposes of comparison in FIG. 1 appended hereto. It can be seen that the actual resistance R of the slag bath falls off more or less steeply, depending on the tip length h.sub.s of the electrode, as the depth of immersion s increases, dropping all the more steeply as the length of the electrode tip is reduced. The knowledge of this relationship is important in designing the power supply and of the electrode feed control, and also to the operation of the electroslag remelting furnace. On the basis of the curves, slight changes in the depth of immersion, especially in the case of short electrode tips, produce fluctuations of the resultant bath resistance. When controlled-current power supplies are used in production apparatus, allowance must be made for this fact by providing for appropriate voltage reserves in the power supply to assure the operation of the current regulator at all times. Furthermore, the dynamic performance of this current regulator must be set up in accordance with the variation of the electrical furnace circuit time constant resulting from the variations of the bath resistance.
The above situation can be expressed by saying that, on the basis of the "immersion curves" or resistance curves, there is a considerable variation in the amplification factor of the regulating system. The calibration of the electrode feed control is therefore performed, for reasons of stability, for the steep portion of the curves. In this portion, outstanding regulation properties result, i.e., especially in the case of shallow slight immersion and a short tip length h.sub.s on the electrode. This has the disadvantage that, for the flatter portion of the characteristic curves there will be a lower control circuit amplification, which will result in inaccurate control in this portion of the curve.